We propose experiments to continue our studies on the effects of low-level microwave irradiation on neurological functions in the rat. In previous research, we found that acute exposure to low- level microwaves affected sodium-dependent high-affinity choline uptake, a measure of cholinergic activity in neural tissue, in various regions of the rat brain. Since cholinergic systems in the brain serve important functions, we will use this effect as the dependent variable to study the (interaction effects of different parameters of irradiation: power density, duration, pulsed versus continuous-wave irradiation, and circularly versus plane-polarized waves. Functional consequence of microwave-induced changes in cholinergic activity in the brain will be investigated by studying radial-arm maze performance, a measure of short-term spatial memory. Possible reversal of the learning deficit by treatment with narcotic antagonists will be investigated. Long-term changes in neural functions after repeated exposure will be investigated by measurements of muscarinic cholinergic receptor properties in different regions of the brain. Involvements of other neurotransmitters in the effects of microwaves on central cholinergic activity will be studied by treating animals with various transmitter antagonists before exposure. Data from our research also indicate that some of the neurological effects of low-level microwave exposure are mediated by endogenous opioids. We propose a series of experiments to measure the levels of three types of endogenous opioids: beta-endorphin, met- enkephalin, and leu-enkephalin, in different regions of the brain after acute or repeated exposure to microwaves. It is hoped that results from this proposed research will further our understanding of the neurochemical mechanism mediating the neurological effects of low-level microwave irradiation and the behavioral consequence of these effects.